Preparation of heat sink materials

ABSTRACT

Portable refrigeration devices including methods for preparing heat sink materials for use in such devices, and the heat sink materials prepared in this way. The methods relate to the encapsulation of such materials, and the maximization of heat transfer efficiency to heat sink materials in such refrigeration devices.

This application is a 371 of PCT/US00/04637 Feb. 24, 2000 which is a CONon 60/121,762 Feb. 26, 1999.

BACKGROUND OF THE INVENTION

The invention relates to self-refrigerating devices employingevaporation/condensation processes. Specifically the invention relatesto methods for the preparation of heat sink materials useful in suchdevices, and the heat sink materials resulting from these preparationmethods.

Self-refrigerating devices are known in the art. These devices aredesigned to provide cooling without resort to external sources ofcooling such as electricity, ice and the like. These devices can also bedesigned to be highly portable. Conveniently, they are designed todeliver cooling on a single-use basis, and are therefore disposable.

Many products, including liquid products, have more favorable propertieswhen cold than when at ambient temperatures. Thus, cooling of theseproducts to temperatures of between about 0° C. and 20° C. is desirable.Generally, such cooling is carried out by electrically-poweredrefrigeration units, or by means of a phase change material such as ice.The use of these units to cool such foods and beverages is not alwayspractical because refrigerators generally require a source ofelectricity, they are not usually portable, and they do not cool thefood or beverage quickly.

An alternate method for providing a cooled material on demand is to useportable insulated containers. However, these containers function merelyto maintain the previous temperature of the food or beverage placedinside them, or they require the use of ice cubes to provide the desiredcooling effect. When used in conjunction with ice, insulated containersare much more bulky and heavy than the food or beverage. Moreover, inmany locations, ice may not be readily available when the cooling actionis required.

Ice cubes have also been used independently to cool food or beveragesrapidly. However, use of ice independently for cooling is oftenundesirable because ice may be stored only for limited periods above 0°C. Moreover, ice may not be available when the cooling action isdesired.

In addition to food and beverage cooling, there are a number of otherapplications for which a portable cooling device is extremely desirable.These include medical applications, including cooling of tissues ororgans; preparation of cold compresses and cryogenic destruction oftissues as part of surgical procedures; industrial applications,including production of cold water or other liquids upon demand;preservation of biological specimens; cooling of protective clothing;and cosmetic applications. A portable cooling apparatus could havewidespread utility in all these areas.

Most attempts to build a self-contained miniaturized cooling device havedepended on the use of a refrigerant liquid stored at a pressure aboveatmospheric pressure, so that the refrigerant vapor could be releaseddirectly to the atmosphere. Unfortunately, many available refrigerantliquids for such a system are either flammable, toxic, harmful to theenvironment, or exist in liquid form at such high pressures that theyrepresent an explosion hazard in quantities suitable for the intendedpurpose. Conversely, other available refrigerant liquids acceptable fordischarge into the atmosphere (such as carbon dioxide) have relativelylow heat capacities and latent heats of vaporization. As a result, somecooling devices which release carbon dioxide are more bulky than iscommercially acceptable for a portable device.

An alternate procedure for providing a cooling effect in a portabledevice is to absorb or adsorb the refrigerant vapor in a chamberseparate from the chamber in which the evaporation takes place. In sucha system, the refrigerant liquid boils under reduced pressure in asealed chamber and absorbs heat from its surroundings. The vaporgenerated from the boiling liquid is continuously removed from the firstchamber and discharged into a second chamber containing a desiccant orsorbent that absorbs the vapor.

SUMMARY OF THE INVENTION

The invention provides methods for the preparation of heat sinkmaterials used in evaporation/condensation-type self-refrigeratingdevices, and heat sink materials which are produced with these methods.The invention is born out of the requirement for high efficiency heattransfer from sorbents found in such devices to the heat sink material.The refrigerant devices require economical, mass production ofvacuum-impermeable, encapsulated phase change material of similar size,shape and density to the sorbent material used in such devices. Theinvention provides a method for a large scale manufacturing of a heatsink material within the needs and constraints of refrigeration unitssubstantially as previously described in U.S. patent application Ser.No. PCT/US00/04639 (publication number WO 00/50824) entitled “Dispersionof Refrigerant Material”, filed contemporaneously herewith, and U.S.patent application Ser. No. PCT/US00/04634 (publication number WO00/50823), entitled “Preparation of Refrigerant Materials”, filedcontemporaneously herewith, both incorporated by reference in theirentirety.

In one aspect, the invention provides a method for preparing heat sinkmaterial for a portable, single-use, non-releasing evaporation-typerefrigerator that produces a refrigerant vapor during evaporativeheating. The method includes providing a quantity of phase change heatsink material (which can under go a phase change at a temperature of,for example, between about 50° C. and about 75° C. having a soliddensity, and which undergoes a volume change (for example, between 10and 25%, or between 12 and 20%) upon it phase change, adjusting thedensity of the heat sink material to a new density which is less thanthe solid density by a percentage, which is within 2% of the percentagevolume change experienced by the phase change material when it melts.The method further includes encapsulating the heat sink material at thenew density, for example in a metallic layer, for example, between0.0005 and 0.002 inches thick, or a polymeric layer, for example,carried out by a radiation-induced polymerization, such as a UV-lightinduced polymerization, for example, with light having an energy in therange of from about 280 nm to about 420 nm. This type of encapsulationcan be carried out using UV-curable epoxy resin-based monomers. Theencapsulation can be accomplished by placing the phase change materialin a substantially gas-and fluid-tight capsule. The encapsulated heatsink material is then placed in thermal contact with a sorbent material,which receives refrigerant vapor during operation of the refrigerator,subsequently evolving heat. The phase change material can be, forexample, paraffin hydrocarbons, sodium acetate trihydrate, sodiumthiosulfate pentahydrate, and disodium phosphate dodecahydrate.

In another aspect, the invention provides a method for preparing heatsink material for a portable, single-use, non-releasing evaporation-typerefrigerator that produces a refrigerant vapor during evaporativeheating. The method includes providing falling drops of a phasechange-type heat sink material from a drop tower apparatus, passingthese falling drops through a volume of IN-curable monomer, providingUV-light of energy and intensity sufficient to cure the UV-curablemonomers, so as to produce a polymer-encapsulated falling drop of heatsink material, breaking the fall of the polymer-encapsulated heat sinkmaterial, placing the polymer-encapsulated heat sink material in thermalcontact with a sorbent material. The sorbent material is designed toreceive refrigerant vapor during operation of the refrigerator,subsequently evolving heat.

In another aspect, the invention provides a method of cooling a productwith a portable, single-use, non-releasing evaporation-type refrigeratorthat produces refrigerant vapor during evaporative heating. The methodincludes providing a portable, single-use, non-releasingevaporation-type refrigerator including an evaporator chamber in thermalcontact with a product to be cooled, ˜vherein the evaporator chambercomprises a refrigerant, dispersed in intimate contact with arefrigerant dispersant, an evacuated sorber in thermal contact with asolid phase change-type heat sink material, wherein the sorber comprisesa sorbent, wherein the solid phase change type heat sink material isencapsulated at a density which is a percentage less than its soliddensity, wherein the percentage is within 2% of the percentage changeexperienced by the phase change material upon phase change, a means forpreventing refrigerant vapor flow between the evaporator chamber and thesorber, until operation of the device; operating the means forpreventing refrigerant vapor flow, thereby permitting the flow, wherebythe pressure in the evaporator chamber is reduced, causing therefrigerant to vaporize and form a refrigerant vapor, the vaporcollected by the sorbent material in the sorber, and heat is generatedin the sorbent, removing the vapor from the evaporator chamber bycollecting the vapor until an equilibrium is reached, wherein thesorbent is substantially saturated or substantially all the refrigeranthas been collected in the sorbent material, and containing the heatgenerated in the sorbent within the sorber by means of the phasechange-type heat sink material.

The invention provides a self-contained and disposable refrigerationdevice. The device according to the invention does not vent a gas orvapor of any kind. There are no hazardous or toxic materials orcomponents included in the device, and recycling of the materials of thedevice is facilitated. There are no pressurized gases present in thedevice and no enviromentally objectionable materials such as unstablerefrigerants. The device does not explode, even when consumed by fire,and is not flammable.

As used in the specification, the term “solid density” refers to thedensity a single crystal of a solid material would have, if the materialis crystalline. In other instances, the solid density refers to thedensity an ideally compacted sample of the solid would have. As used inthe specification, the terms “polymeric”, “polymers” and“polymerization” include the corresponding materials and methods usingblock and random copolymers.

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. Although methods and materialssimilar or equivalent to those described herein can be used in thepractice of the present invention, suitable methods and materials aredescribed below. All publications, patent applications, patents, andother references mentioned herein are incorporated by reference in theirentirety. In case of conflict, the present specification, includingdefinitions, will control. In addition, the materials, methods, andexamples are illustrative only and not intended to be limiting.

Other features and advantages of the invention will be apparent from thefollowing detailed description, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a refrigeration device useful incertain embodiments of the invention.

FIG. 2 is a schematic diagram of evaporation and cooling processesoccurring at the evaporation chamber during operation of a particularembodiment of the refrigeration device.

FIG. 3 is a perspective view of a circular arrangement of evaporatorfingers which can be used in particular embodiments of the invention.

FIG. 4 is a perspective view of a concentric circular arrangement ofevaporator fingers which can be used in particular embodiments of theinvention.

FIG. 5 is a perspective view of a cruciform arrangement of evaporatorfingers which can be used in particular embodiments of the invention.

FIG. 6 is an overhead view of a particular embodiment of a sorberemploying a rib and arch, self-supporting structure.

DETAILED DESCRIPTION OF THE INVENTION

The self-refrigerating device used in the present invention includesthree basic sections: an evaporator chamber containing a refrigerant, anevacuated sorbent chamber containing a sorbent and a heat sink material,and a means to prevent the flow of refrigerant vapor between theevaporator chamber and the sorbent chamber. This flow-preventing meansis also adapted to allow the flow of refrigerant vapor between theevaporator and sorbent chambers, such as when the device is inoperation. The functional relationships between these sections in aparticular refrigeration device have been roughly described in U.S. Pat.Nos. 5,197,302 and 5,048,301. The inventive devices are generallyutilized in conjunction with a product to be cooled. These products andassociated uses will be detailed after discussion of the device itself,which follows directly below.

Regarding FIG. 1, a particular embodiment of refrigeration device Iaccording to the general principles of the invention is displayed. Thisview shows product 5, which is to be cooled, in contact with evaporator10. Evaporator 10 comprises a chamber within which evaporation of arefrigerant takes place. This generally involves desorption ofrefrigerant from a surface during the operation of the device. Beforethe device is activated, the refrigerant is present in the evaporator,both in liquid and vaporous states. In devices such as the presentinvention, this desorption is driven by a pressure differential which ismanifested when a flow-preventing means 44 is operated. Thus, activationof the device amounts to allowing refrigerant vapor flow. Adsorptiontakes place from inner surface 12 of evaporator chamber 10, the outersurface 14 becomes cold. This in turn is able to cool product 5 inthermal contact with outer evaporator surface 14. This is represented inFIG. 2, showing the desorption of refrigerant (H₂O) proceeding indirection 18 leading toward lower pressure. This lower pressure isexposed to the refrigerant upon operation of the refrigeration device,as explained herein.

A wide variety of refrigerants are operative in the device. The generalrequirements are that the refrigerants be vaporizable and condensable atpressures which can be relatively easily attained in chambers. Therefrigerant must also be compatible with the sorbent, that is, it mustbe capable of being absorbed or adsorbed by the sorbent. Suitablechoices for refrigerants must also be those which are able to produce auseful change in temperature in a short time, meet government safetystandards, and be relatively compace. The refrigerants used in thedevices of the present invention preferably have a high vapor pressureat ambient temperature, so that a reduction of pressure will result in ahigh vapor production rate. The vapor pressure of the refrigerant at 20°C. is preferably at least about 9 mmHg. Moreover, for some applications(such as cooling of food products), the refrigerant should conform toapplicable government standards in case any discharge into thesurroundings, accidental or otherwise, occurs. Refrigerants withsuitable characteristics for various uses of the invention include:various alcohols, such as methyl alcohol and ethyl alcohol; ketones oraldehydes, such as acetone and acetaldehyde; ammonia; water; short chainhydrocarbons and short chain halo-hydrocarbons; and freons, such asfreon C318, 114, 21, 11, 114B2, 113 and 112. A preferred refrigerant iswater.

In addition, the refrigerant may be mixed with an effective quantity ofa miscible nucleating agent having a greater vapor pressure than therefrigerant to promote ebullition so that the refrigerant evaporateseven more quickly and smoothly, and so that supercooling of therefrigerant does not occur. Suitable nucleating agents include ethylalcohol, acetone, methyl alcohol, propyl alcohol and isobutyl alcohol,all of which are miscible with water. For example, a combination of anucleating agent with a compatible refrigerant might be a combination of5% ethyl alcohol in water. The nucleating agent preferably has a vaporpressure at 25° C. of at least about 25 mm Hg. Alternatively, solidnucleating agents may be used, such as the conventional boiling stonesused in chemical laboratory applications.

The desorption processes taking place in the evaporator chamber are mostefficiently carried out if the layer of refrigerant is as thin aspossible, to the limit of a monolayer of refrigerant spread over as muchof the inner desorption chamber surface as possible. These thin filmsmaximize the area for surface evaporation. Multiple layers ofrefrigerant cause heat transfer through layered refrigerant molecules toa refrigerant molecule which is disposed at the innermost surface of theevaporator. This type of refrigerant overloading results in atemperature difference across the refrigerant layer that is larger thanwould exist if the layer were thinner. Thus, overloading decreases heatconduction, reducing the efficiency of evaporation. In preferredembodiments with thin layers of refrigerant, the layer thickness isreduced as the refrigeration device operates, decreasing the temperaturedifference across the layer, improving heat conduction processes as therefrigerator operates. If a refrigerant dispersant is employed, this isalso desirably layered as thinly as possible across as much of theinternal evaporator chamber surface as possible.

FIG. 2 shows the desorption of refrigerant (H₂O) proceeding in direction18 leading toward lower pressure. This lower pressure is exposed to therefrigerant upon operation of the refrigeration device, as explainedherein. The particular embodiment illustrated in FIG. 2 uses water asthe refrigerant, but the principles discussed will be applicable tovaporizable refrigerants in general.

The refrigeration devices according to the invention contain a fixedamount of non-circulating refrigerant. If the amount of product to becooled and the amount of cooling desired are known, the amount of heatto be removed is easily calculated. The amount of heat to be removedspecifies precisely the amount of refrigerant which must be evaporatedfrom the evaporator chamber. For example, if 8 fluid ounces (236 mL) ofan aqueous liquid is to be cooled by 22° C., about 8.9 grams of waterrefrigerant is needed as a theoretical minimum. If heat leaks back intothe system, more refrigerant will be required.

As mentioned above, the refrigerant desirably forms a layer on innersurface 12 of evaporator 10. This layer of refrigerant is preferablysubstantially evenly distributed over as much of surface 12 as possible.In certain embodiments of the invention, such as the one shown in FIG.2, this will be accomplished with the aid of refrigerant dispersant 16,which is preferably deposited in a layer on inner evaporator chambersurface 12, and covers as much of this surface as possible. The layer ofdispersant is adapted to allow refrigerant to be absorbed into and/oradsorbed onto it. A variety of materials are available as refrigerantdispersants, as detailed in U.S. patent application Ser. No.PCT/US00/04639 (publication number WO 00/50824) entitled “Dispersion ofRefrigerant Materials”, filed contemporaneously herewith andincorporated by reference in its entirety. In such an arrangement, heatflows from the product across the wall of the evacuator chamber, acrossa layer of refrigerant dispersant, and then vaporizes the surfacerefrigerant molecules from the dispersant.

In selecting the refrigerant dispersant, any of a number of materialsmay be chosen, depending upon the requirements of the system and theparticular refrigerant being used. The refrigerant dispersant may besomething as simple as cloth or fabric having an affinity for therefrigerant and a substantial wicking ability. Thus, for example, whenthe refrigerant is water, the refrigerant dispersant may be cloth,sheets, felt or flocking material which may be comprised of cotton,filter material, natural cellulose, regenerated cellulose, cellulosederivatives, blotting paper or any other suitable material. It isimportant that the refrigerant dispersant be able to be applied to asurface which is highly thermally conductive, such as a metal-containingsurface.

The most preferred refrigerant dispersant would be highly hydrophilic,such as gel-forming polymers which would be capable of coating theinterior surface of the evaporation chamber. Such materials are recited,and methods for their preparation are given in U.S. patent applicationSer. No. PCT/US00/04639 (publication number WO 00/50824), entitled“Dispersion of Refrigerant Materials”, filed contemporaneously herewith,and incorporated by reference in its entirety.

The refrigerant dispersant may be sprayed, flocked, or otherwise, coatedor applied onto the interior surface of the evaporator chamber. In apreferred embodiment, the refrigerant dispersant electrostaticallydeposited onto that surface. In another embodiment, the refrigerantdispersant is mixed with a suitable solvent, such as a non-aqueoussolvent, and then the solution is applied to the interior surface of theevaporator chamber.

In another preferred embodiment, the refrigerant dispersant is able tocontrol any violent boiling of the evaporator and thus reduces anyliquid entrainment in the vapor phase. In such an embodiment, therefrigerant dispersant is a polymer forming a porous space-filing orsponge-like structure, and it may fill all or part of the evaporatorchamber.

In the particular embodiment shown in FIG. 1, evaporator 10 has fins 20and a central passage 22, although a wide variety of shapes andconfigurations of the evaporator are possible. If fins are used, theycan he of a large variety of configurations, and the central passage maybe omitted or substantially shortened. In other embodiments, evaporator10 takes the form of a number of hollow finger-like elements (fingers24) which do not branch from a central passage as do fins 20, but passinto finger base 26, shown in FIGS. 4-6. Base 26 can contain shortpassages (not shown) to connect the interior of hollow fingers 24together to form a short central passage. Alternatively, base 26 can besubstantially hollow, with a central outlet leading to the means forpreventing/allowing vapor flow to the sorbent chamber. Fingers 24 can bearranged in a circle (eight fingers are shown in this arrangement inFIG. 3, but any number could be so arranged), a number of concentriccircles (shown in FIG. 4), in a cruciform arrangement (shown in FIG. 5),or a more random arrangement. The general aim is to provide forefficient heat transfer from the bulk medium to inner evaporator 12, bymaximizing the area of this surface. The evaporator is desirably alsoreasonably simple to manufacture and assemble. Additionally, refrigerantvapor flow paths inside the evaporator chamber are desirably adequate toprevent excessive pressure drops in the low density vapor flows.

Normal boiling processes (ebullition), which are initiated by streams oftiny bubbles rising from discrete and easily visible spots on surfaces,require nucleation sites consisting of reentrant cavities containingnon-condensable gases such as air. The evaporator chamber inrefrigerators according to the present invention is subjected to partialevacuation, effectively removing nucleation sites from the internalsurfaces of the evaporator chamber, and degasses the refrigerant aswell. Thus, refrigerant molecules subjected to the evacuator chamberpreparation methods (as detailed in U.S. patent application Ser. No.PCT/US00/04639 (publication number WO 00/50824), entitled “Dispersion ofRefrigerant Materials”, filed contemporaneously herewith andincorporated by reference in its entirety), which can also be used inrefrigerator devices of the present invention, when exposed to thereduced pressure present in a properly prepared sorbent chamber (asdiscussed below) evaporate from the surface of a quiescent pool ofrefrigerant. Heat transfer in such a pool is subject to the samelimitations of conduction and convection as in bulk fluids.

The refrigerant vapor pressure within the evaporator chamber at thebeginning and end of the cooling process can be determined from theequilibrium vapor pressure temperature function for water, based on theexpected beverage temperatures and temperature differences required forheat transfer.

It is desirable to carry out an evacuation of the refrigerant-loadedevaporator chamber prior to assembly. The evacuation should be limitedto pressures above or equal to the vapor pressure of water at thetemperature at which the evacuation is carried out. For example, at roomtemperature with water as the refrigerant, the evacuation of therefrigerant-loaded evaporator should be carried out to pressures ofabout 20 Torr. This evacuation serves to sweep contaminants such as air,wash solvents and the like from the evaporator chamber.

Returning to FIG. 1, there is also shown sorber 30. This section of therefrigeration device includes sorbent 32, which is disposed throughoutthe interior of sorbent chamber 34. Also included in sorber 30 is heatsink 40. Refrigerant vapor which is formed upon operation of therefrigeration device moves from the evaporator chamber into sorbentchamber 34, carrying heat. This heat is deposited into finite capacitysorbent 32, and further deposited into finite capacity heat sink 40.

The sorbent receives heat not only from the latent heat of vaporizationresulting from condensation of the refrigerant vapor, but also from thechemical reaction heat released when refrigerant is combined with thesorbent. Sorbent 32 is in thermal contact with heat sink 40, viainternal surface 36 and external surface 38 of sorbent chamber 34. Thisthermal contact desirably results in highly efficient heat transfer fromsorbent 32 to heat sink 40. This heat must be stored in the heat sink insuch a manner that it does not leak back into the product during thetime that cold product is required.

Gas molecules tend to adhere to surfaces. Sorbent materials can haveporous structures with a very large surface area per unit volume. Thevolume of non-condensable materials becomes significant in systemsrequiring final pressures below 220 to 500 milliTorr. As an example, acontainer filled with molecular sieve (a typical sorbent) can beevacuated at room temperature to a pressure of from about 1 to 5milliTorr day after day, but will rise in pressure over a few hours toas much as 500 milliTorr between serial evacuations. This rise isattributable to the gradual desorption of sorbed gas molecules. It isunlikely that an economical high production rate refrigeration devicecould incorporate such a process in its manufacture. Since the sorptionprocess in the sorbent acts as a pump to draw vapor from the evaporatorduring operation of the device, the refrigerant vapor pressure over thesorbent must at all times be well below the equilibrium saturationpressure of refrigerant in the evaporator. Essential to the usefulnessof sorbents in the refrigeration devices discussed herein is the removalof non-condensable gases from the refrigeration system. The presence ofnon-condensable gases must be avoided anywhere in the system, for suchgases are carried by the flowing refrigerant vapor into the sorbent, orcould be already present in the sorbent. The presence of non-condensablegases forms a barrier through which refrigerant vapor must diffusebefore it can condense. If such gases are present, the refrigerationdevice will operate at a rate which is limited by the diffusion barrier.

In a similar way, the sorbent must be made as free of condensable gasesas possible before the device is operated. The volume of the sorbent isdesirably minimized for some preferred embodiments of the invention.Thus, competition between refrigerant and a condensable gas alreadypresent in the sorbent will also limit the operation of therefrigeration device to levels below optimum performance. Methods forpreparing various sorbents for use in refrigeration devices are detailedin U.S. patent application Ser. No. PCT/US00/04634 (publication numberWO 00/50823), entitled “Preparation of Refrigerant Materials”, filedcontemporaneously herewith, and incorporated by reference in itsentirety.

The sorbent chamber into which the sorbent is to be loaded also includesa heat sink material. The function of the heat sink material is toabsorb heat released by the sorbent, and to prevent leakage of this heatback to the product which is to be cooled by the refrigeration device.Thus, it is critical to maximize the thermal contact between the sorbentand the heat sink material.

Materials which are suitable as sorbents are those which have aggressiverefrigerant vapor-binding properties, low chemical reaction heats, andare not explosive, flammable or toxic. These materials can be availablein a variety of forms, including flakes, powders, granules, as well assupported on inert shapes or bound with clays. It is desirable that thematerial have sufficient vapor flow passages through it thatrefrigeration performance is not limited by the passage of refrigerantvapor through the sorbent. Additionally, the sorbent must be able totransfer heat to the heat sink material, and thus be in good thermalcontact with the inner surface of the sorbent chamber. Preferredsorbents for use in the present refrigeration device include flakedsorbent or clay-supported sorbent. The latter is available in a widevariety of shapes, including spheres, chips, rectangular solids. Thesorbent chamber into which the sorbent is to be loaded also includes aheat sink material. The function of the heat sink material is to absorbheat released by the sorbent, and to prevent leakage of this heat backto the product which is to be cooled by the refrigeration device. Thus,it is critical to maximize the thermal contact between the sorbent andthe heat sink material. This can be accomplished by ensuring thatsorbent is in good physical contact with the inner surface of thesorbent chamber.

Synthetic zeolite materials comprising metallic alumino silicates can beused in the present refrigeration devices. These materials include awater absorbing mineral supported by a porous inert clay. Such materialsmust be heated to drive absorbed and adsorbed water from them. Theamount of sorbent required to absorb refrigerant vapor depends on thesorption capability of the sorbent for the refrigerant vapor. This isgenerally a function of temperature.

The refrigeration device of the present invention also includes a heatsink located in the sorber. The heat sink is in thermal contact with theouter surface of the sorbert chamber, and thus is in thermal contactwith the sorbent.

The heat-removing material may be one of three types: (1) a materialthat undergoes a change of phase when heat is applied; (2) a materialthat has a heat capacity greater than the sorbent; or (3) a materialthat undergoes an endothermic reaction when brought in contact with theliquid refrigerant.

Suitable phase change materials for particular applications may beselected from paraffin, naphthalene, sulphur, hydrated calcium chloride,bromocamphor, cetyl alcohol, cyanimede, eleudic acid, laurie acid,hydrated sodium silicate, sodium thiosulfate pentahydrate, disodiumphosphate, hydrated sodium carbonate, hydrated calcium nitrate,Glauber's salt, potassium, sodium and magnesium acetate, includinghydrated forms of these materials, such as sodium acetate trihydrate,and disodium phosphate dodecahydrate. The phase change materials removesome of the heat from the sorbent material simply through storage ofsensible heat. In other words, they heat up as the sorbent heats up,removing heat from the sorbent. However, the most effective function ofthe phase change material is in the phase change itself. An extremelylarge quantity of heat can be absorbed by a suitable phase changematerial in connection with the phase change (i.e., change from a solidphase to a liquid phase, or change from a liquid phase to a vaporphase). There is typically no change in the temperature of the phasechange material during the phase change, despite the relativelysubstantial amount of heat required to effect the change; which heat isabsorbed during the change. Phase change materials which change from asolid to a liquid, absorbing from the sorbent their latent heat offusion, are the most practical in a closed system. However, a phasechange material changing from a liquid to a vapor is also feasible.Thus, an environmentally-safe liquid could be provided in a separatecontainer (not shown) in contact with the sorbent material (to absorbheat therefrom) but vented in such a way that the boiling phase changematerial carries heat away from the sorbent material and entirely out ofthe system.

Another requirement of any of the phase change materials is that theychange phase at a temperature greater than the expected ambienttemperature of the material to be cooled, but less than the temperatureachieved by the sorbent material upon absorption of a substantialfraction (i.e., one-third or one-quarter) of the refrigerant liquid.Thus, for example, in most devices according to the present inventionwhich are intended for use in cooling material such as food or beverage,the phase change material could change phase at a temperature aboveabout 30° C., preferably above 35° C., but preferably below about 70°C., and most preferably below 60° C. Of course, in some applications,substantially higher or lower phase change temperatures may bedesirable. Indeed, many phase change materials with phase changetemperatures as high as 90° C., or 110° C. may be appropriate in certainsystems.

Materials that have a heat capacity greater than that of the sorbentsimply provide a thermal mass in contact with the sorbent that does noteffect the total amount of heat in the system, but reduces thetemperature differential between the material being cooled and thesorber, with two results.

When heat is added to a material which doesn't melt or evaporate as aresult of that heat addition, the heat can be sensed by an increase intemperature. By contrast, if the material undergoes a phase change, fromsolid to liquid for example, the material can absorb heat without asensible temperature change. The heat energy instead goes into the phasechange of the material. The hidden heat is referred to as latent heat.Heat sink materials useful in the present refrigeration device are allmelting materials, they absorb significant latent heat, and are able tokeep the sorbent at a more even temperature. The cooler the sorbent, themore vapor it can condense, so it is the combined volume of heat sinkand sorbent that is of direct interest. A low density material and ahigh density material may, in principle, has equal total heat capacity,but a refrigeration device utilizing the low density material willrequire more volume. This increased volume can be undesirable in certaincritical applications.

Some of the heat sink materials considered useful in the presentinvention will undergo a volume change upon phase transition. Forexample, a solid phase change-type heat sink material can change involume by anywhere from 1% to about 30%. For most materials this changein volume is an increase experienced upon phase change. This can presenta problem if encapsulation of such materials is desired. The capsulesmust either be flexible enough to maintain their structural integrity,or a dead volume must be left in place so that expansion will notrupture a more rigid capsule. One way to overcome this problem is tochange the density of a solid phase change-type heat sink material by anamount which is roughly equal to the volume change experienced by thephase change material upon its phase change. For the refrigerationdevices of the present invention, as heat is transferred from sorbent tothe solid phase change-type heat sink material, the heat sink materialmelts. Some of the heat sink materials useful in the present inventionexperience a volume increase upon melting. For example, sodium acetatetrihydrate undergoes an approximately 17% volume increase upon melting.By decreasing the density (e.g., by introducing void volume within thesolid) of the solid sodium acetate trihydrate by approximately 17%before encapsulation, the volume will not change upon melting, andminimal pressure will be exerted upon the capsule. Slight variations inthis density change will be tolerated to the extent that the capsule canwithstand a volume change of its contents.

The density can be changed by applying large compacting forces to thematerial. For example, a pressure of up to 24,000 pounds can be appliedto a compacted granular heat sink material to increase its density tothe desired value, which, in the case of sodium acetate trihydrate, isabout 83% of the solid density (density of a crystal of the heat sinkmaterial, with no void volume). Coupons or pills of sodium acetatetrihydrate, when compressed to this density, appear solid and are strongenough to be easily handled for further processing.

Encapsulation of the heat sink material must be carried out to excludecontaminant materials, such as air or other gases, or water which candegrade the performance of the heat sink. The encapsulation can becarried out by a number of methods including roll coating, metal foilbarriers, spray coating, and other methods known to those skilled in theart.

One encapsulation method which is useful for the encapsulation of heatsink materials makes use of a drop tower and W-curable monomers. Theresult of this process is a polymer-coated heat sink material. Heat sinkmaterial is partitioned into particles such as flakes, crystals, pelletsor drops and placed at the top of a drop tower. The individual particlesare passed, or allowed to fall, through a solution of UV-curablemonomer, so as to entirely coat the particles, preferably individually.The monomer-coated particles of heat sink material are then exposed toUV light of sufficient energy and intensity to cure the monomers into apolymeric coating of the particles. This is a W-induced polymerizationwhich can take place on a time scale of a few seconds. The UV-curablemonomers which can be used in the practice of this aspect of theinvention are epoxy-based resins, olefins such as vinyl monomers andvinylic monomers, epoxy monomers, and alkyl-, aryl-, andamino-substituted derivatives of these monomers. These processes mayrequire the use of sensitizers, which help to initiate the reactions,usually involving singlet or triplet radical or biradical production.These processes can be carried out generally with light energy in theenergy region of from about 220 nm to about 460 nm, or from about 280 nmto about 420 nm. Light intensities should be sufficient to affectpolymerization of the monomer to a continuous layer around the heat sinkmaterial within 30 seconds, preferably within 15 seconds or mostpreferably within 5 seconds. The monomer-coated particles generallycontinue to fall through the drop tower as the photopolymerizationproceeds. They may be maintained in suspension in the light path of thetower by means such as an updraft of air or other gas, at roomtemperature or at a temperature which will accelerate or decelerate thereaction as desired. Upon formation of the polymer coating, theparticles are collected at the bottom of the drop tower. The coatingmust be of sufficient strength to allow for handling, and to account forany expansion or contraction that the phase change-type heat sinkmaterial undergoes during its phase change.

The amount of heat sink material required depends on the amount ofrefrigerant vapor to be absorbed or adsorbed by the sorbent, thechemical reaction heat of the sorbent and refrigerant vapor bindingreaction, the specific heat of the heat sink (or specific heat-latentheat combination in a phase-change material), and the chosen finaltemperature of the sorber. Since some sorbents decrease in refrigerantvapor sorption capability as the temperature increases, there is a ratioof sorbent to heat sink which yields minimum system mass, and whichdepends on the properties of the chosen pair.

The methods of producing heat sink material and the heat sink materialsdescribed herein are useful not only for the refrigeration devicesdescribed, but also for other refrigeration devices, such as thosedisclosed in U.S. Pat. Nos. 5,197,302 and 5,048,301.

The refrigeration device also includes a means for preventingrefrigerant vapor flow from the evaporator chamber to the sorbentchamber before operation of the device. Upon activation of this means,which subsequently allows the foxy of refrigerant vapor from theevaporator chamber to the sorbent chamber, desorption and cooling ofproduct begins. The means for preventing vapor flow can take the form ofany of the various types shown in the prior art. The means can belocated at any location between the evaporator chamber and the sorber,so long as it prevents refrigerant vapor, or vapor of any kind frombeing sorbed by the sorbent. However, if the entire refrigeration deviceis contained within a pressurized container, a pressure responsive valvecan be used which can actuate the device upon the release of thepressure within the container.

The device can be constructed of a variety of materials, with therestriction that certain portions must be able to afford good thermalcontact with certain other portions. These portions must be made of arelatively good thermal conductor such as a metal or metallic material.Preferred materials for the evaporator chamber, and sorber includemetals such as aluminum, copper, tin, steel, and metal alloys such asaluminum alloy. For some applications, corrosion protection will berequired on the outer surface of the evaporator. Corrosion protectioncan include a thin coating of a lacquer specially designed for thatpurpose. Those of skill in the art will be able to provide suitablematerials. The thickness of such coatings generally does not interferewith thermal transfer, but the choice of corrosion protectant will bedictated by the affect such protectant has on the heat transfer.Portions of the refrigerator which are not crucial to thermal transferinclude the means for preventing/allowing refrigerant vapor flow. Thisportion can be made of a polymeric material, such as a thermoplasticmaterial.

The refrigerators are subjected to external pressure, since they areevacuated internally. In order to avoid the necessity of fabricating aheavy structure, self-supporting arch designs or ribbed designs can beused. Materials with similar gauge to those employed in the constructionof carbonated beverage cans are able to find application in theconstruction of the inventive refrigerators. A particular embodiment ofa self-supporting arch design is depicted in FIG. 6. Sorber 30 is shownhaving sorber 32 and heat sink material 40 included in its interior. Onouter surface 46 of sorber 30 are a series of spacers 48. They generallycontinue around the circumference of surface 46, but some are omittedfrom FIG. 6 for clarity. There is intermediate material 50, which can bea polymeric material such as a thermoplastic, attached to spacers 48across the entire circumference of surface 46. The assembly is meant tobe placed in a cylindrical product container, with the terminal portionsof spacers 48 abutting the inner walls of the cylindrical productcontainer. This assembly assists the sorber to maintain its structure,preventing collapse from pressure inequalities between the interior andexterior of the sorber.

The product which can be cooled can be a liquid, gas or solid, as longas good thermal contact is made with the outer surface of theevaporator. Preferred products to he cooled are liquids or gases, mostpreferably liquids. Among the liquids which can be cooled using therefrigeration device of the invention are those comprising water, suchas those comprising at least 20% water, those comprising at least 40%water, and those comprising at least 60% water. Included among suchwater-containing liquids are water itself, milk, fruit and vegetablejuices, soft-drinks, beer, wine, and mixed drinks. These products can becontained in vessels of various sizes and shapes, and those made ofvarious materials. As mentioned above, certain applications will involv⁵the cooling of liquids which can, over lengthy storage times, corrodethe containers in which they are stored. Corrosion protection, known tothose skilled in the art, is available in such instances.

The invention also includes a method of using the refrigeration devicedescribed herein. The method includes the step of providing arefrigeration device of the type set fort herein, opening the means forpreventing vapor flow, whereby the pressure in the evaporator isreduced, causing the refrigerant to be vaporized, which vapor iscollected by the sorbent, removing the vapor from the evaporator bycollecting the vapor until an equilibrium condition is reached whereinthe sorbent is substantially saturated or substantially all therefrigerant originally in the evaporator chamber has been collected inthe sorbent, and simultaneously removing heat from the sorbent by meansof the heat sink material described above. The process is preferably aone-shot process; thus, opening the means for preventing/allowing flowis preferably irreversible. At the same time, the system is a closedsystem; in other words, the refrigerant does not escape from the system,and ther is no means by which the refrigerant or the sorbent may escapeeither the evaporator chamber or the sorber.

OTHER EMBODIMENTS

It is to be understood that while the invention has been described inconjunction with the detailed description thereof, the foregoingdescription is intended to illustrate and not limit the scope of theinvention, which is defined by the scope of the appended claims. Otheraspects, advantages, and modifications are within the scope of thefollowing claims.

1. A method for preparing heat sink material for a portable, single-use,non-releasing evaporation-type refrigerator that produces a refrigerantvapor during evaporative heating, the method comprising: A) providing aquantity of solid phase change heat sink material having a soliddensity, and undergoing a volume increase upon melting; B) adjusting thedensity of said phase change heat sink material to a new density whichis lesser than the solid density by a percentage, wherein the percentageis within 2% of the percentage volume increase experienced by the phasechange material upon melting; C) encapsulating said solid phase changematerial at the new density, wherein the encapsulation is accomplishedby placing the phase change material in a substantially gas- andfluid-tight capsule from which contaminants that degrade the performanceof the phase change material are excluded; and D) placing theencapsulated heat sink material in thermal contact with a sorbentmaterial, wherein the sorbent material receives refrigerant vapor duringoperation of said refrigerator, subsequently evolving heat.
 2. Themethod of claim 1, wherein the phase change heat sink material undergoesa phase change at a temperature between about 50° C. and about 75° C. 3.The method of claim 1, wherein the density to which the heat sinkmaterial is decreased is between 10 and 25% lesser than the soliddensity.
 4. The method of claim 3, wherein the density to which the heatsink material is decreased is between 12 and 20% lesser than the soliddensity.
 5. The method of claim 1, wherein the substantially gas- andfluid-tight capsule comprises a metallic layer.
 6. The method of claim5, wherein the metallic layer is between 0.0005 and 0.002 inches thick.7. The method of claim 1, wherein the substantially gas- and fluid-tightcapsule comprises a polymeric layer.
 8. The method of claim 7, whereinencapsulation with a polymeric layer is carried out by aradiation-induced polymerization.
 9. The method of claim 8, wherein theradiation-induced polymerization is a UV-light induced polymerization.10. The method of claim 9, wherein the UV-light has energy in the rangeof from about 280 nm to about 420 nm.
 11. The method of claim 1, whereinthe polymer is made from at least one UV-curable epoxy resin-basedmonomer.
 12. The method of claim 1, wherein the heat sink material isselected from the group consisting of paraffin hydrocarbons, sodiumacetate trihydrate, sodium thiosulfate pentahydrate, and disodiumphosphate dodecahydrate.
 13. The method of claim 1, wherein the heatsink material is selected from the group consisting of paraffinhydrocarbon, sodium acetate trihydrate, and disodium phosphatedodecahydrate.
 14. An encapsulated heat sink material made according tothe method of claim
 1. 15. A method for preparing heat sink material fora portable, single-use, non-releasing evaporation-type refrigerator thatproduces a refrigerant vapor during evaporative heating, the methodcomprising: A) providing falling drops of phase change-type heat sinkmaterial from a drop tower apparatus; B) passing said falling dropsthrough a volume of UV-curable monomer; C) providing UV-light of energyand intensity sufficient to cure said UV-curable monomer, so as toproduce a polymer-encapsulated falling drop of heat sink material; D)breaking the fall of said polymer-encapsulated heat sink material; E)placing said polymer-encapsulated heat sink material in thermal contactwith a sorbent material, wherein the sorbent material receivesrefrigerant vapor during operation of said refrigerator, subsequentlyevolving heat.
 16. The method of claim 15, wherein the UV-curablemonomer is a epoxy resin-based monomer.
 17. The method of claim 15,wherein the UV-light has energy in the range of from about 220 nm toabout 460 nm.
 18. An encapsulated heat sink material made according tothe method of claim
 15. 19. A method of cooling a product with aportable, single-use, non-releasing evaporation-type refrigerator thatproduces refrigerant vapor during evaporative heating, the methodcomprising: A) providing a portable, single-use, non-releasingevaporation-type refrigerator comprising: 1) an evaporator chamber inthermal contact with a product to be cooled, wherein the evaporatorchamber comprises a refrigerant, dispersed in intimate contact with arefrigerant dispersant; 2) an evacuated sorber in thermal contact with asolid phase change-type heat sink material that undergoes a volumeincrease on melting, wherein the sorber comprises a sorbent, wherein thesolid phase change type heat sink material is encapsulated to theexclusion of contaminants that degrade the performance of the heat sinkmaterial at a density which is a percentage less than its solid density,wherein the percentage is within 2% of the percentage volume increaseexperienced by the material upon melting; 3) a means for preventingrefrigerant vapor flow between the evaporator chamber and the sorber,until operation of the device; B) operating the means for preventingrefrigerant vapor flow, thereby permitting said flow, whereby thepressure in the evaporator chamber is reduced, causing the refrigerantto vaporize and form a refrigerant vapor, the vapor collected by thesorbent material in the sorber, and heat is generated in the sorbent; C)removing the vapor from the evaporator chamber by collecting the vaporuntil an equilibrium is reached, wherein the sorbent is substantiallysaturated or substantially all the refrigerant has been collected in thesorbent material; and D) containing the heat generated in the sorbentwithin the sorber by means of the phase change-type heat sink material.